Lightly grease an 8-9 inch springform pan.In a small bowl, combine the graham cracker crumbs and butter and mix until combined. Dump the mixture out into the prepared pan and use your hands to press the crumbs into the bottom of the pan until you have a smooth, even crust.Add the ice cream and peanut butter to a large mixing bowl. Using a spatula, mix the ice cream and peanut together until the peanut butter is swirled throughout the ice cream. Spoon the ice cream right on top of the crust and smooth it out into an even layer. Cover the cake with plastic wrap, pressing the wrap against the ice cream to help prevent ice from forming. Freeze for 4-6 hours or overnight.To make the fudge sauce. In a microwave safe bowl, microwave the sweetened condensed milk until warm to touch, stirring every 30 seconds. Stir un the chocolate chips until melted and smooth. Remove the plastic wrap and drizzle the fudge sauce over the ice cream cake. Return to the freeze for another 30 minutes. When ready to serve, top the cake with marshmallows or dollop with meringue. Using a blow torch, toast the marshmallow. Slice and serve immediately.